It has become common practice to employ reset timers for controlling industrial machinery and processes. These reset timers generally include a face plate having a window which indicates the digits of the timing cycle. These digits may be manually changed by repeatedly depressing buttons adjacent each exhibited digit. After the timing cycle has been set, the timer repeatedly times the cycle corresponding to the setting appearing at the face plate of the unit. Generally, the visually displayed digits are the numbers on the periphery of axially spaced resettable wheel assemblies. During the counting cycle, digits appearing at the face of the timer count down in generally decimal fashion until reaching all zeros. At this time, the cycle is completed and can be repeated. This type of reset timer has one obvious disadvantage. The timing cycle is not known as the cycle is being timed because the wheel assemblies are counting down during the cycle. In addition, the cycle length for the next cycle can not be changed during a timing cycle of the unit. In order to change the timing cycle, a manual override reset button is often provided. This terminates existing timing cycle and allows the new cycle to be set. In many instances, the termination of a cycle may not be desirable even though a new cycle is desired.
In addition, the reset wheel assemblies used in prior reset timers have often included two relatively movable subwheels one of which is locked in place during the setting and the other of which is movable during the counting and carries the display digits for the counting cycle. There is provided between these two subwheels a cam arrangement which attempts to bring the number carrying subwheel back to a set position after a cycle has been timed and the driving mechanism of the timer is disengaged. This cam return or cam reset mechanism often included a heart-shaped cam wherein the indentation of the heart was the reset position. By this arrangement, a biased follower in one of the subwheels engaged the heart-shaped cam and attempted to bring the two subwheels into a given angular alignment by the action of the cam and the spring biased follower. Excessive wear of the cam and follower mechanism often occurred. This reduced the intended life of the timer. Also, after the follower had moved along the cam for a prolonged time, certain dead spots were sometimes created wherein the numbered wheels would not reset to the proper position by the camming action between the two subwheels. These disadvantages of prior marketed reset timers or counters was overcome by an improved timer/counter unit, which used a magnetic system for returning the number carrying subwheels back to the set or reset position after each timing cycle.
In the prior magnetic return timer or counter there was provided a first bank of manually adjustable number wheels journalled coaxially about a first shaft and arranged from least significant to most significant digits and a second bank of resettable wheel assemblies journalled coaxially about a second shaft generally parallel to the first shaft with one of the wheel assemblies adjacent to and corresponding to one of the number wheels. Each of the number wheels had a gear generally concentric with the first shaft and numerical indicia circumferentially spaced around the first shaft. Separate manual means were provided for indexing the number wheels about the first shaft to selected positions corresponding to a desired counting cycle and means for holding the number wheels in the selected positions. Each of the resettable wheel assemblies included first and second subwheels mounted to rotate about the second shaft. The first subwheel had a gear meshing with the gear of its corresponding number wheel whereby the angular position of the first subwheel about the second axis was determined by the angular position of the gear of its corresponding number wheel. The second subwheel of each wheel assembly included a drive gear coaxial with the second shaft and magnetic biasing or returning means for rotating the second subwheel to a selected position with respect to the first subwheel when the second wheel was released and free to rotate about the second axis whereby the second subwheel of each of the resettable wheel assemblies could return to the position set by its corresponding number wheel. The magnetic biasing or return means includes a first set of permanent magnets carried by the first subwheel and a second set of permanent magnets carried by the second subwheel. These permanent magnets were mutually balanced when the second subwheel was in its selected position with respect to the first subwheel. This provided a magnetic resetting of the driven subwheels to the previously set digital condition of the first subwheel.
The first set of magnets in the first subwheel in the return system of this prior unit were cylindrical, axially magnetized bar-like magnets arranged substantially diametrical with respect to the first subwheel and with radially, outwardly facing, opposite polarity magnetic poles. The second set of magnets were similar to the first set and mounted in the second subwheel so that they would ride in an axially spaced plane with respect to the first set of bar-like magnets. In the balanced condition, the axially spaced sets of permanent bar-like magnets were in magnetic balance with the poles of the magnets facing in different, axially spaced planes. This provided a magnetic return arrangement wherein the magnetic fields surrounding the cylindrical magnets of each set would produce the magnetic balancing forces. This type of magnetic system, for returning one subwheel back to its reset position with respect to the corresponding subwheel, provided a substantial improvement in the art of reset timer/counter unit.